Most affected by this fee increase, set to expire in 2014, are Indian offshore service providers that rely heavily on work visas to deliver services to U.S. customers.

Congress is now considering extending this visa fee increase through 2021 to help cover the cost of the 9/11 responders health care bill, which is now set at $6.2 billion.

In a joint statement this week, Sens. Kirsten Gillibrand and Charles Schumer, both Democrats from New York, said the extension will continue "leveling the playing field between companies that follow the Congressional intent behind these visa programs and companies that use these visas to outsource American jobs."

Schumer, who championed the H-1B and L-1 fee increase to help pay for the $600 million border security bill, argued in August that it creates incentives to hire U.S. workers.

"Our bill will make it more expensive to bring in foreign tech workers to compete with American tech workers for jobs in America. That means these companies are going to have to start to hire U.S. tech workers again," Schumer said.

If the fee increase provided an incentive to hire U.S. workers instead of foreign workers, then revenue from the visas might show a decline over time, as employers used fewer and fewer visas. But the CBO numbers project that the visa revenue will gradually rise, not decline.

The CBO estimates also appear high, especially in the 9/11 bill, and difficult to explain.

The work visa fee increase raises broader questions as well. Will a need for visa fees to help pay for 9/11 health care and border security deter Congress from putting restrictions on the H-1B program for fear of cutting fee revenue?

Will the fee revenue encourage Congress to expand the H-1B visa program beyond its 85,000 cap? The L-1 visas, also subject to the fee increase, are used by multinational companies to move foreign workers into the U.S.

The CBO has set some high revenue expectations for the fee. In the border security bill, the CBO estimated that the visa fee increase will produce $133 million in 2011, with that figure rising to $143 million in 2014. In estimates developed for the 9/11 bill, the CBO said visa revenue will jump to $305 million in 2016 and rise to $311 million in 2020.

The CBO doesn't explain how it arrived at its estimates, and that is prompting head-scratching.